In the field of image analysis and retrieval, it is common to extract local features of an image for comparison against extracted features of other images.
One approach previously considered for extracting local features is the Scale-Invariant Feature Transform (or SIFT) algorithm. Feature vectors extracted with SIFT are invariant to image translation, scaling, and rotation, are partially invariant to illumination changes, and are robust to local geometric distortion. Thus, they can be useful to represent an image for applications such as image matching.